Ken Larsen's website - Light Rail vibration and noise issues

 

Ground-borne noise and vibration are phenomena of all rail transit systems that, if not controlled, can significantly impact residences, hospitals, concert halls, museums, recording studios, and other sensitive land uses. New light rail transit alignments include abandoned railroad rights-of-way passing through adjacent residential developments. Residences located within 3 ft [1 m] of the right-of-way limits are not uncommon, and there are instances where apartment buildings are built directly over light rail systems with little provision for vibration isolation. Vibration impacts on hospitals, sensitive “high-tech” manufacturing facilities, or research facilities may occur. Transit oriented developments (TOD) are attractive, in that they combine commercial and residential structures with transit station structures. In this case, control of structure-borne noise is critical. The most cost-effective mitigation measure for transit-oriented development is to provide a vibration-isolated track, right at the source. 

Ground-borne noise is heard as a low level rumble and may adversely impact residences, hospitals, concert halls, and other areas or land uses where quiet is either desirable or required. Ground-borne vibration in buildings may be felt as a low-frequency floor motion or detected as secondary noise such as rattling windows or dishes. Building owners often claim that ground borne vibration is responsible for building settlement and damage, although no demonstrated cases of this occurring have been verified. Literature concerning rail transit ground-borne noise and vibration control is rich with empirical and theoretical studies conducted in North America, Europe, Australia, the Far East, and South America. A substantial review of the state-of-the-art in ground-borne noise and vibration prediction and control was conducted in 1984 for the U.S. Department of Transportation. Recent research includes studies on the nature of subway/soil interaction, surface track vibration generation, and extensive down-hole testing to assess vibration propagation in soils. The prediction of ground borne noise and vibration has advanced to a highly developed state, relying on shear wave velocity and seismic refraction data, borehole impulse testing, seismic modeling, and detailed finite element modeling of structures and surrounding soils. As a result, vibration predictions can be reasonably accurate. Special track isolation designs are now regularly considered as a means to control perceptible ground vibration in addition to audible ground-borne noise.

9.3.3.12 Distance The track should be located as far from sensitive structures as practicable within the limits of the right-of-way. Where wide rights-of-way exist, some latitude in locating the track may exist. A shift of as little as 10 ft [3 m] away from a sensitive structure may produce a beneficial reduction of vibration for receivers bordering the right-of-way. Sensitive receivers located within 50 ft [15 m] of the track centerline are particularly in danger of being impacted by ground vibration from transit operations. However, ground vibration and ground-borne noise impacts have occurred at sensitive receivers at significantly greater distances. 

4) Highway Grade Crossings Grade crossing warning: based on railroad signaling technology, gates and flashers generally eliminate any need for the LRV operator to slow down to determine if a grade crossing is clear. Grade crossing traffic control based on flashing lights only or even traffic signals only have been employed, but flashers with gates are generally recognized as the most effective type of crossing warning system. Crossing warning indicators are provided ahead of the highway grade crossing to inform the train operator as to the operational status of the highway crossing equipment. 5) Yard and Shop Operational rules and small turnouts generally restrict train operations in yards to low speeds, typically 5 to 10 miles per hour. Busy switches are normally power operated; infrequently used switches are often hand thrown. Signals or indicators are provided where required and can be either integral with or external to the switch machine. Signal system architecture for a yard can be either vital or non-vital design and include track circuits. 

10.2.10.1 General Highway crossing warning systems provide indications to motorists that a light rail vehicle is approaching the crossing. Such systems are commonly but erroneously called crossing “protection” systems. That term is incorrect as there is no way to protect the train from a motor vehicle whose operator elects to ignore the signals and no way to protect the motorist from the consequences of his/her failure to comply with the signals provided. What the signals can do is warn the operator of a motor vehicle on an intersecting path that a train is approaching. Currently, there is no effective way to advise an LRV operator that motor vehicles are approaching a crossing, making it highly desirable to keep the “sight triangles” at all four quadrants clear of obstructions such as buildings and vegetation. The most common configuration for highway crossing warning systems is conventional flashing light signals, either with or without gates, such as those commonly used on freight railroad grade crossings. In determining the type and configuration of the highway crossing warning system, consideration should be given to LRV operations, type of track circuit, roadway layout and posted speeds, traffic signal(s) location, right-of-way, and clearances. The challenge of fail-safe crossing warning systems is to separate the LRV and highway traffic without closing the crossing to motor vehicle traffic for extended periods of time. The Federal Highway Administration’s Manual of Uniform Traffic Control Devices (MUTCD) now includes recommendations for at-grade crossings of LRT tracks. These requirements are included in Part 8 of the MUTCD (2009 edition), which can be downloaded from the FHWA’s website. In some cases, crossing warning systems will include specific signs and warning signals for pedestrians. The track designer needs to coordinate the layout of the crossing surface and the approach pavements so that pedestrians are directed along paths where they can clearly see warning devices. In addition to the requirements currently in the MUTCD, there have been numerous experimental installations of barriers and crossing warning devices to promote the safety of both pedestrians and motorists and, by extension, the operators and passengers of the rail vehicles. One example is active signage that flashes to indicate a “Second Train Coming” from the opposite direction of the one that initially activated the warning system. This issue is dynamic and LRT design teams are encouraged to consult recent trade publications and published papers for state-of-the-art information. Crossing warning installations should be interconnected with any traffic signals located within 200 feet [60 meters] of the highway grade crossing. Additional advance warning of approaching LRVs, i.e., more time than required at an ordinary crossing, may be required for proper operation of the traffic signals so as to “flush” certain legs of the intersection prior to train arrival. An on-site diagnostic team meeting is usually required at an early date to discuss all of the implications of the warning system being proposed. 

 

-Excerpted from TCRP Report 155 (Track Design Report for Light Rail Transit) by Lisa Brach, a Villas of Culp Arbor resident on Farrington Road in southwest Durham


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